feat: remove spawn timer on singleplayer (#3199)

Resolves #1041 

## Description:

Remove the singleplayer spawn countdown so the game starts when the
player spawns, spawn nations immediately after player spawn, and align
game timer/max-timer timing with the new start point.

Added a singleplayer regression test for spawn-immunity timing
(GameImpl.test.ts) and updated spawn-phase loop tests to use gameType:
GameType.Public where singleplayer behavior is not under test (e.g.
MIRV/AI/Spawn/WinCheck-related suites), eliminating inSpawnPhase()
timeout hangs after the new singleplayer start logic.


https://github.com/user-attachments/assets/c07a585f-1153-490e-88ca-a91fc7ae5756

## Please complete the following:

- [x] I have added screenshots for all UI updates
- [x] I process any text displayed to the user through translateText()
and I've added it to the en.json file
- [x] I have added relevant tests to the test directory
- [x] I confirm I have thoroughly tested these changes and take full
responsibility for any bugs introduced

## Please put your Discord username so you can be contacted if a bug or
regression is found:
aotumuri

tests/core/pathfinding/SpatialQuery.test.ts

@@ -16,7 +16,8 @@ function addPlayer(game: Game, tile: TileRef): Player {
   const info = new PlayerInfo("test", PlayerType.Human, null, "test_id");
   game.addPlayer(info);
   game.addExecution(new SpawnExecution("game_id", info, tile));
-  while (game.inSpawnPhase()) game.executeNextTick();
+  game.executeNextTick();
+  game.executeNextTick();
   return game.player(info.id);
 }